In Release-10 specification of long term evolution (LTE) wireless communication standard, the user equipment (UE) feedbacks a channel quality indication (CQI) in addition to a precoding matrix index (PMI) and rank indicator, which correspond to a supported modulation and coding scheme (MCS) level that can be supported reliably by the UE, with a certain target error probability. The feedback designs in Release-10 are designed for single-user multiple-input multiple-output (MIMO) communication techniques.
Multi-user (MU) MIMO corresponds to a transmission scheme, where a transmitter transmits data to two or more UEs using the same time/frequency resource by relying on spatial separation of the corresponding user's channels. With support of up to four transmit (Tx) antennas, transmission scheme designs are typically designed for MU-MIMO support for the case of two user MU-MIMO transmissions with a single stream per each UE.
Accordingly, there is a need for improved communication techniques and standards for supporting MU-MIMO.